1. Field of the Invention
The present invention relates to a field emission display, and more particularly, to a field emission display that includes field emitters made of a carbon-based material having a low work function.
2. Description of the Related Art
A field emission display (FED) is a flat display device that realizes a display of images by using a cold cathode as a source for emitting electrons. Recently, much research has been performed on formation of field emitters, in which a low work function carbon-based material that emits electrons at low voltages of approximately 10 to 15 volts is used to perform a thick layer process such as screen printing.
Where the FED employs a triode structure including a cathode, an anode, and a gate electrode, cathode electrodes and field emitters are formed on a rear substrate, and gate electrodes are formed on the cathode electrodes and emitters with an insulating layer interposed therebetween. Further, an anode electrode and phosphor layers are provided on an inner surface of a front substrate.
However, in the above triode structure, the formation of field emitters through the thick layer process is technically very difficult to perform. That is, to form the field emitters, holes are formed in the gate electrodes and the insulating layer to expose the cathode electrodes, and where performing screen printing of carbon-based material on a surface of the cathode electrodes, which are exposed through the holes, the carbon-based material may be formed extending from the cathode electrodes to the gate electrodes to thereby cause a short between the two electrodes.
FIGS. 17 and 18 show a structure in which gate electrodes 7 are arranged under cathode electrodes 3 and emitters 5 with an insulating layer 1 interposed between the gate electrodes 7 and the pairs of the cathode electrodes 3 and the field emitters 5.
In the FED shown in FIGS. 17 and 18, electric fields are formed in peripheries of the field emitters 5 by a voltage difference between the gate electrodes 7 and the cathode electrodes 3 such that electrons (indicated by the arrows in FIG. 18) are emitted from the field emitters 5. The emitted electrons are accelerated toward a front substrate 11 as a result of a high voltage of approximately 1 to 5 Kv applied to an anode electrode 9 formed on the front substrate 11. The electrons excite phosphor layers 13 formed on the front substrate 11 to thereby realize the display of predetermined images.
With such an FED, the manufacture of the field emitters 5 is easy, and a short does not occur between the gate electrodes 7 and the cathode electrodes 3. However, with the use of this structure, since there is a limited ability to focus electrons emitted from the field emitters 5, the electrons that are emitted from the emitters 5 disperse toward the front substrate 11 while moving within the display such that the emitted electrons land on unintended phosphor layers 13, that is, adjacent phosphor layers 13 of different colors. The unintended electron landings result in a mixture of colors, reducing color purity.
Examining traces of electron beams formed by the emitted electrons in more detail with reference to FIG. 18, as the distance between the field emitters 5 and the phosphor layers 13 increases, the degree of focusing of the electron beams deteriorates. That is, electron beams (2) and (3) are less focused than electron beam (1) and more dispersed in the direction of an axis Y shown in FIG. 18. Further, electron beams (2) and (3), are also dispersed in the direction of axis X as shown in FIG. 17, thereby resulting in the formation roughly of a triangle by the electrons landing on the front substrate 11.
FIG. 19 is an optical microphotograph showing an illumination pattern of actual phosphor layers by the emission of electron beams in a conventional FED. The microphotograph shows that the electron beams landing on the front substrate illuminate the phosphor layers in roughly triangular patterns. Therefore, with the dispersion of the electron beams in both X and Y axis directions in the conventional FED, adjacent phosphor layers of different colors are also illuminated (together with the intended phosphor layer) such that color purity is diminished.
An object of the present invention is to improve color purity of the display device by providing a field emission display in which electrons emitted from field emitters accurately land on phosphor layers of intended pixels rather than on phosphor layers of unintended pixels.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
In one embodiment, the present invention provides a field emission display comprising a front substrate and a rear substrate provided opposing one another with a predetermined gap therebetween; a plurality of gate electrodes formed in a line pattern in a first direction and a plurality of cathode electrodes formed in a line pattern in a second direction, which is perpendicular to the first direction, on a surface of the rear substrate opposing the front substrate; a plurality of field emitters formed on the cathode electrodes at areas corresponding to each pixel region where the gate electrodes intersect the cathode electrodes; an anode electrode formed over an entire surface of the front surface that opposes the rear substrate; and phosphor layers formed on the anode electrode, wherein any one of the field emitters adjacent in one of the first and second directions to another field emitter is at a predetermined distance from the another field emitter in the other of the first and second directions.
The field emitters may include first emitters and second emitters, which are alternately arranged in the direction the cathode electrodes are arranged, the first emitters having a predetermined distance in a direction perpendicular to the direction the cathode electrodes are arranged from the adjacent second emitters to thereby result in a zigzag pattern of the first and second field emitters.
The cathode electrodes may each include first and second sub-electrodes, which are arranged in a line pattern at a predetermined distance, and corresponding connecting electrodes that electrically connect the first and second sub-electrodes. Also, the first emitters may be arranged on long edges of the first sub-electrodes, which are opposite the second sub-electrodes, and the second emitters may be arranged long edges of the second sub-electrodes.
Alternatively, the field emitters include first emitters and second emitters, which are alternately arranged in the direction the gate electrodes are arranged, the first emitters having a predetermined distance in a direction perpendicular to the direction the gate electrodes are arranged from the adjacent second emitters to thereby result in a zigzag pattern of the first and second emitters.
To realize this structure, holes are formed in the cathode electrodes to expose the insulating layer at areas corresponding to each pixel region, and the holes include first and second sides that are parallel to the gate electrodes. Also, the first emitters are formed on the cathode electrodes along the first sides of the holes and the second emitters are formed on the cathode electrodes along the second sides of the holes.